(1 of )The hitch of van that was pulling a trailer with a pizza oven is photographed at the scene of fatal accident on Lakeville Highway near Old Lakeville Highway No. 3 on Friday, August 8, 2014 in Petaluma, California. (BETH SCHLANKER/ The Press Democrat)

Specially trained investigators Monday were examining a pizza oven trailer to determine what caused it to break loose on Lakeville Highway and careen into a car, killing a father of two from Vallejo.

The oven was being pulled by a 1997 Chevy van driven by an employee of Rosso Pizzeria, a Sonoma County restaurant and catering company. Driver Edward Jacobson, 46, of Petaluma was returning from an event Friday evening when the trailer hitch somehow failed, Rosso co-owner Kevin Cronin said.

Cronin said he doesn’t yet know how the oven broke free. Investigators on Monday were inspecting the towing components, including whether safety chains were hooked up.

The oven slammed into a Honda driven by Dwayne Usher, 32, who died at the scene. Usher’s two sons, ages 4 and 8, as well as a woman in the front seat were also injured.

“We’re devastated,” said Cronin. “I’ve been spending most of my time saying prayers for the family.”

Usher’s grandmother Ruthie Usher of Vallejo said her family was reeling from the loss.

“He was the best father to them boys,” Ruthie Usher said.

Rosso owns three pizza oven trailers that are frequently seen at Sonoma County farmers markets and catered events. Cronin said Rosso is working with its insurance company and the CHP to learn more about what took place.

“We’re trying to get as much information as possible,” he said.

The oven was impounded and taken to Cloverdale Tow, CHP Officer and spokesman Jon Sloat said.

The crash took place at about 7:20 p.m. Friday.

Jacobson was driving north on Lakeville Highway when the oven disconnected and slammed into Usher’s car.

Usher was stopped on Old Lakeville Road No. 3 at its intersection with Lakeville Highway and the impact caused both the car and trailer to overturn.

Usher’s 8-year-old son, Devin, was flown to Children’s Hospital Oakland, where the child remained Monday. His younger child Anthony, 4, was treated at Santa Rosa Memorial Hospital and released, hospital staff said. Front-seat passenger Ariel Motta, 34, was also taken to Santa Rosa Memorial Hospital according to the CHP. Hospital staff said they had no information about Motta.

You can reach Staff Writer Julie Johnson at 521-5220 or julie.johnson@press democrat.com. On Twitter @jjreport.